1. Field of the Invention
The present invention relates to multilayer electronic components and methods for manufacturing the same.
2. Description of the Related Art
A multilayer ceramic condenser (hereinafter, MLCC) is manufactured by printing a conductive paste on the formed dielectric layer sheet with screen, gravure, or other methods to print an internal electrode layer and laminating the sheet on which the internal electrode layer is printed.
The conductive paste used at this time mainly consists of inorganic matter such as metal powder such as Ni and Cu and ceramic powder (inhibitor) and organic matter such as dispersants, resins, additives, and solvents.
Generally, since the metal powder used in the internal electrode paste, such as Ni and Cu, has a lower melting point than ceramic powder used in a dielectric layer, a temperature at which sintering shrinkage starts is low. Therefore, since ceramic powder is added as an inhibitor to shift a shrinkage start temperature to high temperature to be similar to that of a dielectric as much as possible and the ceramic powder used as an inhibitor is absorbed into the dielectric layer in the process of firing the internal electrode layer to ultimately contribute to dielectric characteristics, the inhibitor is designed with the same or similar composition to the dielectric layer. In the general case, barium titanate (BaTiO3), which is the same as the composition of the dielectric layer, is used as a main component of the inhibitor, and various oxide sub-components may be used to increase a sintering start temperature.
An internal electrode is sintered through the following process in manufacture of an MLCC.
A step in which an inhibitor leaks out while metal power shrinks at 800 to 1000° C. (1). A step in which an internal electrode layer is connected while a dielectric layer shrinks at 1000 to 1100° C. (2). A step in which the internal electrode layer is agglomerated while the dielectric layer becomes dense at more than 1100° C. (3).
Therefore, as a sintering temperature is increased, electrode disconnection is increased, and as particulate metal powder is used for thinning, electrode disconnection is more increased.
In the conventional methods, electrode connectivity is improved by using ceramic powder with the same or smaller size than that of metal powder used in an internal electrode layer as an inhibitor to restrain contact between the metal powders and thus increase a shrinkage start temperature of the internal electrode.
Generally, since an inhibitor is absorbed into a dielectric layer after firing to ultimately contribute to dielectric characteristics, it is designed with the same or similar composition to the dielectric layer. Further, since the inhibitor should be distributed between metal particles to limit sintering, it has generally a smaller particle size than metal powder and the amount thereof is adjusted according to a firing temperature of a chip.
In the MLCC, the inhibitor component added to the internal electrode layer moves to the dielectric layer during sintering to affect the characteristics of the dielectric. Since ultrathin/ultrahigh capacity MLCCs include a thin dielectric, the effect of the inhibitor component is great.
According to the trend of high capacity and thinning of the MLCC, the internal electrode layer as well as the dielectric layer becomes thinner, and a thinner internal electrode is needed. However, unless a firing temperature of the dielectric is remarkably reduced, as an internal electrode becomes thinner, it is difficult to form an internal electrode with excellent connectivity.
Therefore, an inhibitor is added to the internal electrode layer to suppress the sintering shrinkage of the internal electrode. The thinner the internal electrode is, the greater the effect of the inhibitor is. When many oxygen vacancies are formed on the interface between the electrode and the dielectric, electrical characteristics such as withstand characteristics, accelerated life, and capacity are badly affected.
The role of the inhibitor is to lower a temperature at which sintering shrinkage starts as much as possible. However, when the sintering of metal used as an internal electrode starts, most of the inhibitors are pushed out to the dielectric layer or some of them are trapped between the metal and the inhibitors pushed out to the dielectric layer react with the dielectric layer so that firing is performed.
Therefore, a layer greatly influenced by the inhibitor component (hereinafter, inhibitor-influencing layer 30a and 30b) is formed on the interface of the dielectric layer 10 close to the internal electrode layer 20a and 20b. In case of ultrahigh capacity/thin MLCCs, a fraction of the interface layer is increased.
The inhibitor uses barium titanate (BaTiO3, BT) with a smaller size than Ni used in the internal electrode as a main component, and BT has smaller size and lower crystallinity than BT powder applied to the dielectric layer. And since the interface between the dielectric and the electrode is used as a path for removing a binder during firing, a reducing atmosphere acts relatively. Therefore, the layer influenced by the inhibitor has relatively high frequency of oxygen vacancies and deteriorates withstand voltage characteristics, reliability, and capacity characteristics.